Process for melting light metals and alloys thereof in electricalinduction furnaces



sept. s, 1925. 1,552,865

T. METZGER PROCESS FOR MELTING LIGHT METALS AND ALLOYS THEREOF INELECTRICAL INDUCTION FURNACES Filed April 22, 1924 Patented Sept. 8,1925.

UNITED STATES 1,552,865 PATENT OFFICE.

THOMAS METZGER, 0F DUSSELDORF-GERRESHEIM, GERMANY.

- 'PROCESS FOR MELTING LIGHT METALS AND ALLO'YS THEREOF IN ELECTRICAL-INDUCTION FURNACES. A

Application led April 22, 1924. Serial No. 708,259.

according to the construction and the form and dimensions of thecomponent parts of the furnace, especially of the melting grooves. Thesaid phenomenon was partly utilized in certain types of furnaces for thepurpose of agitating thel metal bath, but in most instances suchphenomenon was considered a rather undersirable disturbing of thecurrent exciter and of the regularity specific gravity of the saidmaterial.

in the movement of the material to be molten. Of late, endeavors weremade in order to avoid the occurrence of such phenomenon as far aspossible or otherwise to reduce its effect to such an extent, that thelatter would cause no harm. Said Pinch eli'ect consisting in thecontraction of the mass through which the current passes, and which willeven cause a total interruption of the band of the mass tobe molten, isthe more powerful the higher the densityvof current in the materialto-be molten, and the lower the For that reason a certain relationbetween the level of the melting bath in the melting chambers-filledwith material and through which it will flow and the specific gravity ofthe mass must exist or must be effected in electrical melting furnaces,in vwhich the bath and the melting groove connected horizontally orvertically or inclined with the bath .forms the induced secondarycircuit, that is to say, it is necessary to arrange.

the melting bath extending in the said type of furnace to the meltinggroove, at such a level, that the static pressure caused by the gravityof the mass will be sufficient for obtaining the desired success asregards the Pinch effect in the lower and narrower places, e. g. themost endangered points.

`Said gravity and the cross-sectional load on the mass to be molten,which depends on the value of the specific gravity of the latter, willcause an action adverse to the said Pinch effect, in so far as provisionis made, as soon as the said Pinch effect commences totake action on thematerial, that is to say, as soon as an open space is formed or going tobe formed, which does not contain any material, that such empty spacesformed or forming are filled up from above, so that to a certain degreethe said Pinch effect is neutralized from the beginning. This purpose isattained to a sufficient degree at present with a series of furnaceshaving narrow melting grooves, for heavy metals, as for instance copper,brass and zinc, by giving the furnace such dimensions that it will showa handy and economical form and size.

If the same type of furnace is used for melting light metals, as forinst-ance magnesium, or aluminium` or alloys thereof in particular,electron and the like, it would be necessary to give the furnace and themelting groove in particular for the purpose of imparting to the moltenlight metal the required high static pressure by its own gravity, such aconstruction and height, that an economical working of the plant wouldno longer be possible, since the proportional value of the head or topweight in respect of the radiating surface would become toounsatisfactoryand the useful effect of the furnace obtainable be reducedtoo far. Besides, the furnace would necessarily attain such verticaldimensions, that it would be difficult to attend and operate it, and inaddition too large a space would be required for the erection of suchfurnace. Owingl to the high conductivity of light metals, which withaluminium is 21/2 times as large as with brass, in a furnace constructedaccording to the same principles for brass melting only relatively smallintensity of current and energy could be applied and consequently prettylong melting periods would be required, so that for the reasons statedworkingY of 4such furnace would prove too uneconomical.

In order to provide equally favorable conditions in respect of theapplication of sufficiently high intensity of current, favorabledimensions as well as economy in operating `the furnace according totheinvention, such furnace mustbe of such construction that the meltingrocess is accomplished, whilst the interior space of said of the heatedmass.

It has been suggested to work electrical melting furnaces for Zinc andalloys containing zinc in such a manner that during the melting step thefurnace is subjected to a far higher gas pressure, but this suggestionwas hardly ever reduced to practice. It is intended in this instance toraise the boiling point of the material considerably in order to preventthe formation of lzinc vapors and their noxious consequences; thus ameasure of entirely different purpose and result is concerned, as in theforegoing case. In the latter case for instance with aluminium, theinterval between the melting point (625 degrees) and the boiling pointA(230() degrees) is ahoy/t 1700 degrees centigrade and the danger of theformation of metal vapors does not exist.` Therefore not the employmentof high pressures of gas (from 4 to 12 atmospheres) is concerned, but amoderate pressure figuring as a rule below one atmosphere. Whilst theformer are handled with-difficulty only in view of the construction ofthe furnace, especially as regards the former tightness of the jacketsand closures, the process according to the present invention dealingw-ith low pressures only, is easily to be carried out.

In order to reduce the furnace to equal dimensions and output and inorder to be able to apply a suiiiciently high density of current, itwill do to subject the melting bath to about the pressure indicated, inorder to overcome the Pinch effect. simultaneously.

In the accompanying drawing an induc tion furnace having a meltinggroove, is illustrated by way of example, which is suitable for theprocess above described,

F is the melting chamber from which extends a vertical melting groove G,which is connected in known manner with the main hearth for the materialto be molten. K is the refractory furnace lining in the interior, saidfurnace being closed atthe top by means of a cover.v The furnace is ofthe tilting type and possesses a tap hole C and at B the chargingopening closedby a door.

H is the transformer iron and J the primary coil. The melting bath isshown by broken lines. The furnace is provided all round with a mantleor jacket, the connec- 'with the furnace and which cocks can be set insuch position, that the gas can leave the furnace chamber. As is showndiagrammatically the said cocks are positively connected at E with theconnection doors.' On moving the said doors an automatic locking willtake place, so that the cocks A and AI respectively are closed and thepressure passes through A and A1 into the open air, previous to openingthe doors C or B. In a similar manner by means of a device brought intoconnection with the cocks and the rods E respectively the supply ofcurrent to the furnace can be interrupted, if or before A or A1 isturned into blow-off' position.

I claim:

l. A process for melting aluminum, magnesium like light met-al andalloys thereof' in induction furnaces, consisting in filling theinterior of the furnace above the melt bath with neutral gas at suchpressure that the pressure of the molten metal increased by the gaspressure results in a total pressure in the secondary circuiteliminating or reducing to a minimum the Pinch effect in the melt.

2. A process for melting aluminum, magnesium and like light metals andalloys thereof in induction furnaces, consisting in filling the interiorof the furnace above the melt bath with gas at such pressure that thepressure of the molten metal increased by the gas pressure results in atotal pressure in the secondary circuit eliminating or reducing to aminimum the Pinch effect in the melt.

ln testimony whereof I have affixed my signature.

THOMAS METZGER.

